Renal Cysts

Renal cysts are fluid collections that form in the kidneys; it is not clear what causes them. They may occur if the kidney surface becomes less resistant, forming a kind of diverticulum that fills with fluid, creating the cyst.

The older you are, the greater the chance of cysts being detected.

They are detected incidentally during routine exams, most often ultrasound. Simple renal cysts do not cause symptoms and do not need to be treated.

Generally, cysts are simple and rarely lead to complications. Typically, a cyst occurs in one kidney, on its surface; eventually, multiple cysts may appear in both kidneys. These are different from those seen in the condition known as polycystic kidney disease, which is fortunately rarer.

Up to 27–50% of people over 50 years of age have simple, asymptomatic renal cysts.

Complications that can be caused by cysts (very rare):

- Infected cyst: may cause pain and fever

- Cyst rupture: for example, in closed trauma, it may cause acute pain in the abdomen or flank.

- Urinary obstruction: when a large cyst blocks the passage of urine, leading to kidney dilation.

Simple cysts must be differentiated from possible renal tumors that may appear as complex cysts.

This differentiation is easily characterized today by a well-performed radiological study, whether an ultrasound, or with better characterization a CT scan or MRI, the latter being ideal for small lesions/nodules.

According to their appearance, they are classified by the Bosniak grading system, named after the author who described it.

Bosniak I (practically 0% malignancy)

Bosniak II (practically 0% malignancy)

Bosniak IIF (around 5% malignancy)

Bosniak III (more than 50% malignancy)

Bosniak IV (practically all malignant)

Cysts with Bosniak III and IV classification have a formal indication for surgical treatment, removal of these by laparoscopic surgery or today's gold standard – robot-assisted surgery.